The present invention generally relates to a vehicle transmission system, and more particularly to a vehicle transmission system and method of operating a vehicle transmission system for controlling the temperature of torque transmitting devices.
A vehicle transmission generally includes a number of gear elements coupling an input drive shaft and an output drive shaft, and a related number of torque-transmitting devices, which shall also be referred to as clutches, that are formed of one or more components such as bands, plates, rings, seals, fluids, springs, retainer and ball assemblies and/or brakes, which are selectively engaged and disengaged to select particular gear elements and establish an operating ratio between the input drive shaft and the output drive shaft of the vehicle. The torque-transmitting devices can be of any number of configurations, including band and disc brakes, which are generally known in the art as reaction clutches, brake clutches or application clutches.
The input drive shaft is coupled to the engine of the vehicle, and the output drive shaft is directly coupled to the wheels, propeller or other drive mechanism of the vehicle. Transition or shifting from a first operating ratio, such as a first velocity ratio, to a second operating ratio, such as a second velocity ratio, is performed in response to any number of parameters such as engine load or throttle position, vehicle velocity and/or operator commands. The transition or shift generally involves releasing and disengaging one or more clutches (i.e., off-going) associated with the first operating ratio and applying or engaging one or more clutches (i.e., on-coming) associated with the second operating ratio. This engaging and disengaging action typically increases the temperature of the clutch, and the period that a clutch can be utilized before replacement (i.e., clutch life or clutch durability) is at least partially related to this temperature. For example, a clutch operating at 450xc2x0 F. has an almost unlimited clutch life while a clutch operating at 550xc2x0 F. has a clutch life that has orders of magnitude fewer off-going and on-coming cycles during a clutch life, and a clutch operating at 700xc2x0 F. has yet orders of magnitude fewer off-going and on-coming cycles during a clutch life.
Numerous techniques have been introduced to control the temperature of the clutch and increase the clutch life. For example, hot mode techniques have been introduced to cool the fluid of a transmission. However, additional apparatus and methods for controlling the temperature of the clutch to increase clutch life are continually sought to supplement, enhance and/or replace existing techniques. In addition, methods and apparatus are desired to address excessive and repeated shifts of the transmission by the operator of the vehicle and/or excessive and repeated shifts of the transmission by the control system of the vehicle.
In view of the foregoing, it should be appreciated that it would be desirable to provide a vehicle transmission system and methods of operating a vehicle transmission system that control the clutch temperatures of the transmission system to extend the clutch life. In addition, it should be appreciated that it would be desirable to provide a system and methods that address excessive and repeated shifts of the transmission, which substantially increase clutch temperature and decrease clutch life. Furthermore, additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and following detailed description of a preferred exemplary embodiment and appended claims.
In accordance with the teachings of the present invention, a vehicle transmission system and method of operating a vehicle transmission system are provided that control clutch temperatures to extend the clutch life. The vehicle transmission is comprised of an input drive shaft configured to be driven by an engine of the vehicle, an output drive shaft configured to drive a drive mechanism of the vehicle and a plurality of torque-transmitting devices connecting the input drive shaft to the output drive shaft and configured to engage and disengage to provide a transition between a plurality of operating ratios of the input drive shaft and the output drive shaft. The vehicle transmission system is also comprised of a control module configured to predict a temperature of the plurality of torque-transmitting devices based at least in part upon a shifting status of the plurality of torque-transmitting devices. The control module is further configured to conduct at least a first modification of the operation of the plurality of torque-transmitting devices if the temperature is greater than a first predetermined temperature and a second modification of the operation of the plurality of torque-transmitting devices if the temperature is greater than a second predetermined temperature.